CSMA/CD-type local area networks (LANs) are widely known, particularly the Ethernet and Cheapernet networks. Both of the latter two networks will be referred to in the rest of the text under the umbrella term Ethernet network for the sake of simplicity. They are standardized by the Institute of Electrical and Electronics Engineers (IEEE) in the form of IEEE Standard 802.3 and repeated by the International Standards Organization (ISO) in the form of ISO Standard 8802.3. Ethernet networks have a data transmission speed of around 10 Mbits/s.
Due to the technological development of such networks, more and more data terminals can be connected to them, entailing the development of communication servers within the computers themselves that communicate through these networks. The servers reduce the load of a computer's central processing unit (CPU) by managing some of the messages sent by the different constituent elements of the computer, as well as messages coming from other terminals on the network to which the computer is connected.
The development of the power and processing capacity of CPUs of computers makes it possible to have an increasing number of input/output peripherals communicate with the CPUs. These input/output peripherals are most often synchronous or asynchronous terminals communicating with their outside environment over transmission lines at speeds that can range from 300 bits/s to 2 Mbits/s. The transmission modes and the protocols used on the corresponding transmission links to these terminals are defined, for example, in Notes V-24, V-28, V-11, V-35, V-36 of the CCITT (International Telegraph and Telephone Consultative Committee). These transmission links are provided by transmission elements which are actually distinct cables or pairs of twisted wires.
Large, modern networked computer systems can include up to several hundred terminals connected by many cables or sets of wires to the computer or computers which are part of these large systems. When such terminals are distributed within a geographic site with limited area, the existence of a large number of cables or wires poses mechanical and physical problems and poses major space requirements.
The current practice is usually to connect a given computer system to other systems of the same type as well as to its own input/output terminals using an Ethernet network. The computer's communication server is then connected to the input/output terminals via a large number of adapters whose function is to adjust the transmission flow and the transmission protocol of the Ethernet network to the flows and protocols used on the different transmission lines for each input/output terminal. Such adapters are described, for example, in the French patent application filed on Dec. 20, 1990 under No. 90 16031 entitled "Distributed Computer Architecture Using a CSMA/CD-type Local Network," filed by the applicant, which corresponds to U.S. patent application Ser. No. 07/920,321.
Means are known for remotely locating all the transmission elements constituted by cables or sets of twisted wires outside the geographic space occupied by the computer and its communication server, and these means take up a small amount of geographic space. These means define what can be called a host structure for adapters. Such a structure is described, for example, in French patent application 90 16032 filed by the applicant on Dec. 20, 1990 and entitled "Host Structure for Terminal Adapters Belonging to a Distributed Computer Architecture."
Such a host structure includes a first compartment which contains several cartridges, each of which has a card containing the electronic circuit of an adapter, and a second compartment containing the electrical power supply for the adapter cards contained in the first compartment and containing a ventilation device for the structure.
The first and second compartments are adjacent and separated from one another by a backplane assembly with a bus specific to the network to which the adapters are connected. This backplane assembly provides the ability of connecting the bus to said cards and to the network, on one hand, and to the power supply, on the other. The cartridges are parallel to one another and can be removed. On a front edge, the cartridges have a group of connectors to which are connected the transmission elements leading to each of the terminals associated with the adapter contained in said cartridge. The advantage of such a structure is its modular nature. However, it has the following disadvantage: if an adapter must be changed, each of the cables making the connection with the corresponding terminals must be disconnected before the cartridge containing said adapter is pulled out. This is not very practical and causes handling problems as well as losses of time.